1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor device, and more particularly, to a method for fabricating a gate electrode in a semiconductor device.
2. Description of the Related Art
In a conventional fabrication process of a semiconductor device, a gate electrode of an MOS (Metal Oxide Semiconductor) transistor is fabricated through the following steps.
A gate electrode material is formed to a predetermined thickness on the underlying semiconductor substrate having a gate oxide film interposed therebetween.
Next, the gate electrode material is partially etched to form the gate electrode in a predetermined shape, i.e., a linear shape.
After that, the resultant substrate is subjected to a selective oxidation process, thereby repairing damage caused by the etching process, assuring reliability of the gate oxide film, preventing an electric field from being concentrated on an edge portion beneath the gate electrode, and preventing GIDL (Gate Induced Drain Leakage) due to the gate electrode.
Generally, the gate electrode material is formed of polysilicon having excellent interfacing properties in a high temperature environment with respect to the gate oxide film. However, as semiconductor devices become more highly integrated, the conventional polysilicon gate electrode does not satisfy the requirements for sheet resistance of the gate electrode and operation speed.
Recently, a proposed method for forming a metallic gate electrode in which a refractory metal, for example, tungsten, is stacked on the polysilicon gate electrode. However, since a tungsten film has an undesired active reaction with the underlying polysilicon gate electrode, a conductive barrier film is formed between the tungsten film and the polysilicon gate electrode.
In the method of forming a metallic gate electrode comprised of atungsten film, a conductive film and a polysilicon gate electrode, undesirable oxidation occurs along an edge portion beneath the metallic gate electrode during the selective oxidation process and also oxygen penetrates into an interface between the conductive barrier film and the overlying tungsten film, thereby creating an undesired oxygen-series of amorphous foreign particles.
Also, when a self-aligned contact technology is employed in a cell region, a capping nitride film is formed on the tungsten film. In this case, oxygen penetrates into the interface between the capping nitride film and the underlying tungsten film during the selective oxidation process, thereby creating undesired foreign particles at the interface therebetween.
Accordingly, a disadvantage exists in the above described methods in that undesired alien substances cause an increase in the resistance of the gate electrode.
Further, since oxygen is intruded into and oxidation occurs along the edge portion beneath the linear-shaped metallic gate electrode in the selective oxidation process, a relatively thick oxide film is formed in the edge portion beneath the gate electrode, thereby causing an increase in the threshold voltage of the transistor.
Moreover, as a minimal line width of the gate electrode becomes gradually smaller, oxidation occurs over the lengths of the gate electrode during the selective oxidation process, thereby deteriorating operational properties of the semiconductor device.